Post on 17-Jul-2020
An ancient extrasolar system with fivesub-Earth-size planets
Tiago Campante1,2
1University of Birmingham, UK
2Stellar Astrophysics Centre (SAC), Aarhus University, Denmark
September 18, 2014
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Introducing KOI-3158
also KIC 6278762,HIP 94931
spectral type K0V
over 0.5 arcsec yr−1
V = 8.86
d = 36 pc
iron-poor andoverabundant in αelements (e.g., Siand Ti)
Atmospheric parameters
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A member of the thick disk (I)
thick disk
thin disk
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A member of the thick disk (II)
Toomre diagram
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Possible extragalactic origin?
member of the Arcturusstream
named after Arcturus(brightest star in northerncelestial hemisphere)
these stars travel 2 kpcabove Galactic plane
extragalactic originvs. dynamical origin withinGalaxy
artist’s conception
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Hierarchical triple system
fainter companion at1.8 arcsec
high-resolutionimaging withRobo-AO
3.94 % dilution
the two componentsare co-moving
secondary comprisestwo M dwarfs!
two M dwarfs!
KOI-3158
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Asteroseismic analysis (I)
short cadence: Q4.2, Q6,Q15–17
record-breaking ∆ν at180 µHz
stellar properties fromgrid-based modeling
1.9 % relative precisionon R and 1.1 % on 〈ρ〉
Stellar properties
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Asteroseismic analysis (II)
detailed frequencymodeling
GARSTEC, ASTEC,YREC, MESA, and AMPcodes used
11.2 billion years old!
9 % precision on ageestimate
oldest known system ofterrestrial-size planets
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Transit analysis
4 years oflong-cadence data
five-planet transitmodel
affine-invariantMCMC algorithm
took into accountdilution
KOI-3158.01
KOI-3158.02
KOI-3158.03
KOI-3158.04
KOI-3158.05
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A system of terrestrial-size planets
KOI-3158.01 isMercury-sized
intermediate planets areMars-sized
KOI-3158.05 smaller thanVenus
from the mini-Neptunesaround Kapteyn’s star andKepler-10’s super-Earths tothe terrestrial-size regime
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Highly-compact system
orbital periods under 10days
. . . or within 0.08 AU
period ratios close tostrong 5: 4, 4 : 3, 5 : 4,and 5: 4 first-orderMMRs
system fits within orbitof Kepler-11’s innermostplanet
compact systems makeup ∼1 % of Keplercandidate hosts
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Dynamical evolution
proximity to strong resonances points to dynamical evolution
convergent inward migration is likely mechanism
tides then push planets wide of exact commensurability
will make an interesting case study!
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System validation
only plausible FP of 4planets + 1 backgroundEB rejected at 99.9 %level
no background stars inDSS archival data
non-randomness ofobserved multi-resonantchain
dynamical instability ifplanets were to orbitM-dwarf companion
DSS POSS-I (epoch 1945-58) DSS POSS-II (epoch 1984-99)
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Implications (I)
giant-planet hosts:metal-rich
small-planet hosts: morediverse composition
⇒ terrestrial-size planetsmay have started to formearlier
(sub-)Earth-sizeplanets have formedthroughout most ofUniverse’s history
ancient life in theGalaxy?
Buchhave et al. (2012)
blue: small planets (<4 R⊕)
red: giant planets (>4 R⊕)
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Implications (II)
α elements critical forplanet formation iniron-poor environments
thick-disk starsoverabundant in αelements inlow-metallicity regime
⇒ thick-disk (and high-αhalo) stars were likelyhosts to first Galacticplanets
ancient systemsaround KOI-3158 andKepler-10 helppinpoint beginning ofera of planet formation
Adibekyan et al. (2012)
black line: exoplanet-host trendgreen line: non-host trend
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Acknowledgments
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